The present invention relates to electrical component mounting and wiring assemblies and, more particularly, to sensor mounting assemblies that are connected to and function to terminate a wire cable.
Electrical sensors of various types are used to sense the position of a cooperating structure. In the intrusion alarm industry, sensors are used to detect unauthorized entry by determining the open or closed position of a window or door. The typical sensor includes a magnetically actuated reed switch that is mounted on the window frame or door jamb and which cooperates with a permanent magnet attached to the window or door. The sensor assemblies are mounted at the various `point-of-entry` locations and connected through the wiring system to a central controller which can determine the open or closed state of the window or door.
One type of prior sensor assembly has been fabricated from a printed circuit board to which the magnetically actuated reed switch is physically secured and to which the switch leads are soldered. A fixed-length cable, typically with four conductors, is also soldered to appropriate traces on the printed circuit board to complete the circuit with the reed switch. The switch and circuit board are then positioned within a molded plastic housing and retained in place by an epoxy or silicone potting compound to provide a reliable, weatherproof device.
Another sensor mounting and connection device is disclosed in U.S. Pat. No. 4,679,881 to Galvin et al. and is designed to connect a plurality of sensor devices in series circuit. A box-like structure is provided with spaced, parallel slots and insulation displacement contacts for making electrical contact with the circuit conductors. The individual circuit wires are laid into the slots in general registration with the insulation displacement contacts. A cooperating component is provided with flanges which push the circuit wires into the insulation displacing contacts to establish electrical contact. A knife blade is also provided to sever excess wire to produce the series circuit connection.
The sensing device assemblies typically used in the intrusion alarm industry and their installation methods are generally satisfactory from the functional standpoint, although certain cost and performance drawbacks are present as a consequence of the manufacturing and installation techniques. For example, the sensor assemblies that use a printed circuit board and soldered connections must be fabricated in a production-type environment as contrasted to assembly in the field at the point of installation. The need to manufacture each sensor assembly with a fixed-length lead that is subsequently trimmed to length results in wasted cable and associated costs at the time of installation. These costs are increased when high-temperature PTFE insulation is used on the circuit wiring. Likewise, the splicing of the trimmed cable to the system wiring requires an additional increment of time on the part of skilled workers at the point of installation and, in some installations, such as store merchandise windows, the presence of junction boxes is aesthetically undesirable. The sensor assemblies that use insulation displacement contacts do allow circuit fabrication in the field, although the wire receiving slots do not positively retain the wires in place, and external mechanical disturbances of the wires can be transmitted to the insulation displacement contacts. It is known that any relative movement between the insulation displacement contact and its connected wire can adversely disturb the metal-to-metal seal and initiate conditions, such as corrosion couples, which degrade the integrity of the electrical connection. Since the wire conductors are mounted in individual slots accessible from the exterior of the assembly, the wire color-coding is visible, and, accordingly, aspects of the circuit wiring pattern can be ascertained. Lastly, the assembled sensors, especially those that are potted, do not allow convenient electrical probing of the reed switch or other circuit devices during or after installation to effect in-the-field testing.